College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China.
Institut für Mineralogie, University of Münster, Münster 48149, Germany.
Environ Sci Technol. 2020 Jan 7;54(1):207-215. doi: 10.1021/acs.est.9b05145. Epub 2019 Dec 19.
Phosphorus (P) availability is widely assumed to be limited by the formation of metal (Ca, Fe, or Al) phosphate precipitates that are modulated by soil organic matter (SOM), but the SOM-precipitate interactions remain uncertain because of their environmental complexities. Here, we present a model system by quantifying the in situ nanoscale nucleation kinetics of calcium phosphates (Ca-Ps) on mica in environmentally relevant aqueous solutions by liquid-cell atomic force microscopy. We find that Ca-P precipitate formation is slower when humic acid (HA) concentration is higher. High-resolution transmission electron microscopy observations demonstrate that HA strongly stabilizes amorphous calcium phosphate (ACP), delaying its subsequent transformation to thermodynamically more stable phases. Consistent with the formation of molecular organo-mineral bonding, dynamic force spectroscopy measurements display larger binding energies of organic ligands with certain chemical functionalities on HA to the initially formed ACP than to mica that are responsible for stabilization of ACP through stronger HA-ACP interactions. Our results provide direct evidence for the proposed importance of SOM in inhibiting Ca-P precipitation/transformation. We suggest that similar studies of binding strength in SOM-Fe/Al-P may reveal how both organic matter and metal ions control P availability and fate, and thus the eventual P management for agronomical and environmental sustainability.
磷（P）的有效性通常被认为受到金属（Ca、Fe 或 Al）磷酸盐沉淀形成的限制，而这些沉淀又受到土壤有机质（SOM）的调节，但由于环境的复杂性，SOM-沉淀相互作用仍然不确定。在这里，我们通过液相原子力显微镜原位定量测量云母上钙磷酸盐（Ca-Ps）的纳米成核动力学，提出了一个模型系统。我们发现，当腐殖酸（HA）浓度较高时，Ca-P 沉淀物的形成速度较慢。高分辨率透射电子显微镜观察表明，HA 强烈稳定无定形磷酸钙（ACP），延迟其随后向热力学上更稳定的相转变。与分子有机-矿物键的形成一致，动态力谱测量显示，具有某些化学官能团的有机配体与最初形成的 ACP 之间的结合能大于与云母之间的结合能，这是通过更强的 HA-ACP 相互作用来稳定 ACP 的原因。我们的结果为 SOM 在抑制 Ca-P 沉淀/转化方面的重要性提供了直接证据。我们建议，对 SOM-Fe/Al-P 中结合强度的类似研究可能揭示有机质和金属离子如何控制 P 的有效性和归宿，从而最终实现农业和环境可持续性的 P 管理。
